As disclosed, e.g., in U.S. Pat. No. 4,694,100 (Shimizu et al.) and British Patent 1,565,235 (Mitsubishi), it is known that aralkenes, such as 4-isobutylstyrene, can be carboxylated with carbon monoxide and water or an alcohol in the presence of a palladium catalyst under acidic conditions to form an aralkanoic acid or ester, such as ibuprofen. Alperetal., J. Chem. Soc. Chem. Comm., 1983, pp. 1270-1271, disclose a similar reaction employing a mixture of palladium and copper and requiring the presence of oxygen; and European Patent Application 284,310 (Hoechst Celanese) teaches the use of a palladium catalyst in association with a phosphine ligand to accomplish the carboxylation of 1-(4-isobutylphenyl)ethanol to ibuprofen with carbon monoxide in an aqueous acidic medium.
These known processes have been used with some success. However, it would be desirable to develop a process that would not require the presence of oxygen or an acidic medium or the use of an uneconomical starting material like 1-(4-isobutylphenyl)ethanol but would still provide the acid or ester product in good yield.